Phytochrome and endogenous gibberellin-like substances in etiolated and irradiated oat seedlings

The level of gibberellin-like substances was investigated in oat coleoptiles with different stationary states of phytochrome and in leaf segments which had been etiolated and irradiated with red light. Etiolated coleoptiles and leaves containing maximum amounts of the PR form of phytochrome were characterized by an increased level of bound gibberellins. Irradiation with red light resulting in the photoconversion of phytochrome into the Pt R form caused the appearance of a high content of free gibberellins. It seems that the releasing the hormones from bound forms correlated with the formation of phytochrome PFR may be an important aspect of the mechanism of phytochrome action in the processes of seedling deetiolation. The interrelation between phytochrome and plant hormones in the control of photomorphogenesis of young monocotyledonous seedlings is also discussed.

Gibberellin-like substances in embryonic shoots of Scots pine in relation to generative differentiation

Investigations were carried out on embryonic shoots of lateral and terminal buds of Scots pine (<em>Pinus silvestris</em> L.) of different age. at various stages of seasonal devclopment. The results show that there is a correlation between gibberellins content and apical dominance in pine. More are found in terminal buds than in lateral ones. The transition from a juvenile phase into a mature one in Scots pine is accompanied by a lowering of the gibberellin content. The formation of male inflorescences is accompanied by an increased amount of endogenous gibberellins and the appearence of a new group of non-polar gibberellin-like substances. The formation of female cones is connected with the lowering of endogenous gibberellin content.